SettingsLib: Update Android.mk to include test package makefile.

Change-Id: I9d6574ef059872e449abfe47f16f80143bb86aec
Fixes: 31327402
Test: verified that test appears after running 'make continuous_instrumentation_tests dist'
diff --git a/packages/SettingsLib/Android.mk b/packages/SettingsLib/Android.mk
index 1098a8e..ad07283 100644
--- a/packages/SettingsLib/Android.mk
+++ b/packages/SettingsLib/Android.mk
@@ -19,3 +19,6 @@
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 
 include $(BUILD_STATIC_JAVA_LIBRARY)
+
+# For the test package.
+include $(call all-makefiles-under, $(LOCAL_PATH))
\ No newline at end of file